The disclosure relates to articles with a low contrast, anti-reflection coating and more particularly to such articles with reduced surface defect (e.g., scratches and fingerprints) visibility.
Transparent, scratch resistant films and hard coatings are used in the display cover glass market and other applications such as architectural, automotive, or other applications requiring high optical transmission and surface durability. These films and coatings have also been shown to improve the resistance to damage, during drop events onto hard and rough surfaces.
Anti-reflection coatings have also been developed for these markets and applications to reduce the intensity of reflected ambient light from a surface, to increase the transmittance, the readability and viewability of displays, and to reduce unwanted or distracting glare from eyeglasses, windows and other surfaces. Conventional anti-reflection coatings suffer from drawbacks including an increased visibility of surface defects (as described herein) when compared to surfaces with the same surface defects but that do not include an anti-reflection coating. As shown in FIG. 1, the visibility of a surface defect depends at least in part on reflectance contrast between a pristine portion of an anti-reflection coating and surface defect-containing portion of the same anti-reflection coating. FIG. 1 illustrates a known article 10 with a substrate 20 with a surface 22, and anti-reflection coating 30 disposed on the surface 22 forming a coated surface 32. In FIG. 1, the removal of a portion of the anti-reflection coating 30 (i.e., formation of a surface defect on the coated surface 32) forms a new surface that includes a surface defect 34. The coated surface 32 that is free of surface defects is considered pristine. As used herein, the phrase “pristine” means a coated surface that is free of surface defects, as defined herein. As shown in FIG. 1A, the pristine coated surface has a first reflectance % R1 and the surface including a surface defect (shown by the removal of a surface thickness) exhibits a second reflectance % R2 that is different from % R1. Some anti-reflection coatings include alternating high refractive index layers and low refractive index layers, the second reflectance % R2 differs from % R1 because the material at the exposed surface that includes the surface defect 34 is different from the material at the pristine surface. This result is also present when the surface defect includes the addition of a contaminant on the coated surface, instead of the removal of a surface thickness. This difference in reflectance highlights the presence of a surface defect, which may be enhanced by the presence of a surface defect having varying surface thicknesses removed thickness, depending on the structure of the anti-reflection coating.
In addition, recently emerging coating materials for display covers may have high hardness or other improved mechanical properties; however, these improved mechanical properties are often fundamentally associated with materials having a higher refractive index, such as Al2O3, single-crystal Al2O3 (sapphire), AINx, AlOxNy, SiNx, SiOxNy, and ZrO2.
Accordingly, there is a need for specially designed coatings that reduce the reflectance associated with articles with high-index materials and/or transparent substrates, without substantially increasing the visibility of surface defects that may appear or form during use of the articles. The present disclosure relates to reduce reflectance, as compared to the same bare transparent substrates, while reducing visibility of surface defects.